An early version before 2005 of comsol multiphysics was called femlab. If using the windows operating system, this is located in the file menu under help. The result was validated with simple physical arguments. The pdes can be entered directly or using the so called weak form see finite element method for a description of weak formulation. Understanding the weak form will help us gain insight into how the comsol software works internally as well as enable us to write our own equations when there is no builtin interface available for the. Weak contributions are, in fact, what the software internally uses to apply the builtin domain and boundary conditions. When you do, you may wonder what this expression means. In addition to conventional physicsbased user interfaces, comsol multiphysics also allows for entering coupled systems of partial differential equations pdes. The model tree in the model builder gives you a full overview of the model and access to all functionality geometry, mesh, physics settings, boundary conditions, studies, solvers, postprocessing and visualizations. The software described in this document is furnished under a license agreement.
Comsol implementation of a porous media model for simulating. In comsol you can set up your system of equations, adjust it and. In comsol multiphysics, i notice that using the generalized alpha with strictintermediate time steps is the best way to converge my structural based nonlinear solution. Previously in our weak form series, we discretized the weak form equation to obtain a matrix equation to solve for the unknown coefficients in our simple example problem. Convert a general second order linear pde into a weak form for the finite element method. How to use weak form pdes in comsol to solve maxwells. The weights are also called the degrees of freedom in a finite element method. To simulate this system in comsol we need to put it into weak form. How to write the elasticity equation for isotropic solid. I have some knowledge to use simple weak form pdes in comsol. It is important to note that this translation is normally done automatically because comsol multiphysics needs the weak form to proceed with the calculation. Understanding the weak form will help us gain insight into how the comsol software works internally as well as enable us to write our own equations when there is no builtin interface available for the particular physics involved in our model.
Define the linearized weak form for c omsol livelink matlab. Therefore three weak expressions must be defined in comsol instead of the general weak expression for the elasticity equation weak form attached, where u is the displacement vector and w is the. Comsol quick installation guidebasic information for installing the comsol software and getting started. The time derivative expression can actually be entered in the weak term. A point source is a useful tool for idealizing the situation where a source is concentrated in a very small region of the modeling domain.
How do i make a nonlinear solver converge in comsol multiphysics. Adding a global equation to a pde in comsol multiphysics. Comsol new release highlightsinformation about new features and models in the 3. If you have a problem which involves a combination of acoustics, electromagnetics, electrochemistry, optics, molecular flow, microfluidics, etc. A brief introduction to the weak form comsol multiphysics. It gives the mathematical formulation of the problem and the weak form in vectoriel form and axisymmetric form. Weak contribution comsol cfd online discussion forums. However, i wonder that why there is a 2order differential in integrand but only 1 time integral on the left of equation 1. Deriving the weak form for linear elasticity equation. Simulation of sawdriven microparticle acoustophoresis using comsol multiphysics software n. The packages are crossplatform windows, mac, linux.
You will find stepbystep modeling instructions, discussions of a variety of physics, product news, and more on the comsol blog. The full documentation set that ships with comsol multiphysics consists of the following titles. This defines how comsol solves the navier stokes equations in weak form which was your original question. Internally, this will be discretized using finite element interpolation functions based on the shape function picked in the discretization section of the settings window for the weak form pde interface. In this series, we have demonstrated this power by solving problems that include finding the shape of soap films, planning paths for a hiker around a lake, and repairing. How using a comsol multiphysics app helps you analyze matrices during the solution process. I have a problem to develop the weak form pdes of maxwells equations to calculate electric field in comsol.
The weak form we derived above and specified in the comsol multiphysics interface is a continuous problem. We modeled network a using builtin hyperelastic material models in comsol software with no modifications. Costanzo1 1department of engineering science and mechanics, pennsylvania state university, pa, usa 2institute of fluid mechanics and aerodynamics, bundeswehr university munich, neubiberg, germany. The main reason is that we already had a formulation in the weak form that has been implemented in cast3m. However, it is also possible to enter a weak form as a user. For many of the different types of physics simulated with comsol multiphysics, a weak formulation, or weak form, is used behind the scenes to construct the mathematical model. Sep 07, 2017 in order to check that the update installation was successful, first start the comsol multiphysics software and select the about comsol multiphysics menu option.
Finite elements, however, are based on an alternative form, the weak form, which is equivalent to the former. You will need an onsubscription comsol license attached to your comsol access account or a software trial provided by your sales representative. Specifying a weak form of a transient pde involves the following three steps in the weak form pde interface in comsol multiphysics. To request a demonstration, simply fill out the form on this page. Quick question, when i make the weak form of my pde, i end up with domain and surface integrals. Configuration of comsol multiphysics for simulating axisymmetric. These apps can be run with a regular comsol multiphysics license but also with a comsol server license. Do i input both types of integrals in the same spot. For many of the different types of physics simulated with comsol multiphysics, a weak formulation, or weak form, is used behind the scenes to. If you use finite element simulation software, such as comsol multiphysics, you will come across the expression weak form at some point. Watch an introduction video to comsol multiphysics on the developers site, here. Using comsol to solve weak forms in 2d part 1 youtube. If you do not yet have a comsol access account, please create one now. Overview of the comsol multiphysics application modes 2.
Implementing the weak form with a comsol app comsol blog. Substituting them one by one into the weak form equation to obtain the discretized system of equations the resulting matrix equation is sparse, which can be solved efficiently using a computer. Today, we will start to take a behindthescenes look at how the equations are discretized and solved numerically. We continue our weak form blog series with a guide on how to implement and solve these equations numerically in comsol multiphysics. This means that the comsol license server needs to be upgraded to comsol 5. This post continues our blog series on the weak formulation. Configuration of comsol multiphysics for simulating axisymmetric dielectric resonators. Here, you will learn about its basic ideas and corresponding benefits. Today we continue our discussion on the weak formulation by looking at how to implement a point source with the weak form. What is the best way to derive the weak form for pde equation based. Hello, you are right, the dweak term was in the past used for entering the time derivative of the unknown for timedependent problem there is no mathematical dweak form, only a weak form. In the previous post, we implemented and solved an exemplary weak form equation in the comsol multiphysics software. If you still need help with comsol and have an onsubscription license, please. Define the linearized weak form for comsol livelink matlab.
Constitutive modeling of polyethylene in comsol multiphysics. Apr 29, 2014 no equals sign needs to be included, since the weak form pde is automatically set to zero. The weak form, together with the boundary conditions, is then used to formulate a finite algebraic system of equations for the unknowns. All equations are in a weak form with periodic boundary conditions and simple geometries. Feb 25, 2011 adding a global equation to a pde in comsol multiphysics, accumulation of heat example. Implementing the weak form in comsol multiphysics comsol. In addition to conventional physicsbased userinterfaces, comsol multiphysics also allows for entering coupled systems of partial differential equations pdes. If using the linux and macos operating systems, this is located in the help menu. Very glad to learn from your blog on weak form of comsol and its a very good blog specifying on weak form that merely introduced detailedly anywhere.
The pdes can be entered directly or using the socalled weak form see finite element method for a description of weak formulation. The pdes can be entered directly or using the socalled weak form. For network b we explicitly provided the hyperelastic equations, including the weak form, as a function of the elastic component of the deformation gradient. Feb 02, 2018 consider the weak form input this equation in comsol homework equations the attempt at a solution testux expxtestu. Within the model tree, you can view all the equations as they appear in weak form click on view equations in the options. Would you like to see a demonstration of the comsol software in real time. The version of lmgrd must be the same or higher than the flexnet version used by the comsol software. Comsol multiphysics is a generalpurpose platform, based on advanced numerical methods, for modeling and simulating physicsbased problems. Sep 11, 2016 in this video, two dimensional heat transfer problem is solved using comsol multiphysics software.
Are the surface integrals like using boundary conditions. Trial licenses are automatically associated with your account. I am looking to implement a surface stress via a weak contribution in comsol using the twophase flow laminar mesh physics module. In the galerkin finite element method, the shape functions are of the same sort as the test functions. How to implement the weak form for timedependent equations. Comsol multiphysics is a crossplatform finite element analysis, solver and multiphysics simulation software. Comsol will detect the time derivative automatically.
We introduce you to the weak form and showcase its use in comsol multiphysics in this blog series. We describe in this section both the strong and weak forms, and we prove their equivalence. The general weak form for the master equation as joannopoulous calls it is. This course focus on deriving equations of the finite element system and using matlab to obtain the finite element solution, then solving. Could u tell me please how to programme it in the weak form. The weak form is the most general and precise way to specify the equations in a finite element context, and it is this formulation we will use below. Comsol provides an ide and unified workflow for electrical, mechanical, fluid, acoustics and chemical applications. In the previous blog post, when we implemented the weak form equation using comsol multiphysics, the discretization was done under the hood without needing the users help. In addition to conventional physicsbased userinterfaces, comsol multiphysics also allows users to enter coupled systems of partial differential equations pdes directly or by using the socalled weak form. If so, can i not put in the surface integrals and use the built in boundary conditions in comsol. You can also other related materials on the comsol multiphysics course page of my website. It allows conventional physicsbased user interfaces and coupled systems of partial differential equations pdes. How to implement a point source with the weak form. This software is a general finite element code using a script language to implement a model in terms of general building blocks.
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